Selective hydrocracking with a sulfur containing cadmium zeolite catalyst



United States Patent 3,337,447 SELECTIVE HYDROCRACKING WITH A SULFURCONTAINING CADMIUM ZEOLITE CATALYST James Arthur Rigney, Baton Rouge,Ralph Burgess Mason, Denham Springs, and Glen P. Hamper, Baton Rouge,La., assignors to Esso Research and Engineering Company, a corporationof Delaware No Drawing. Filed Sept. 13, 1965, Ser. No. 487,026 22Claims. (Cl. 208-111) This invention relates to the removal ofstraight-chain hydrocarbons from petroleum-derived feedstocks by theirselective conversion in the presence of hydrogen. More particularly, itrelates to a selective hydrocracking process which is accomplished inthe present of a crystalline metallo alumino-silicate having uniformpore openings less than about 6-Angstrom units in diameter, andpreferably about 5 Angstroms.

Hydrocarbon conversion and upgrading with crystalline alumino-silicatezeolite catalysts is now well known in the art. For example, the use ofthese zeolites for hydrocracking has been generally directed to typicalpetroleumderived feedstocks, such as gas oil, etc., which arecustomarily converted to lower boiling products useful as gasoline. Thecrystalline zeolites employed for such purposes usually have uniformpore openings of about 6 to Angstroms and are therefore nonselective;that is, substantially all of the feed molecules are admitted into thezeolite pore structure. For many purpose-s selective hyd-rocracking ofonly certain molecular species is obviously to be desired. One suchpurpose, for example, is the octane improvement of naphtha fractions byselectively hydrocracking only straight-chain hydrocarbons (e.g.,olefins, paraifins, etc.) which tend to be low octane producing, andthereafter removing the hydrocracked products and recovering a higheroctane product. Another purpose is the selective hydrocracking of thestraight-chain hydrocarbon content of lube oil and gas oil fractions forpour point reduction or dewaxing. The use of a nonselective large pore(e.g., 6 to 15 Angstroms) crystalline zeolite for such purposes isineifectual, since desired feed molecules, e.g., aromatics, are admittedinto the zeolite pores and hydrocracked along with the straight-chainhydrocarbons.

With specific regard to the upgrading of naphtha fractions for inclusionin the high quality motor gasoline necessary for modern automobiles, itis customary to improve the octane rating and cleanliness or gum-formingproperties by means of such processes as thermal or catalytic reforming.The desired product is usually of about the same boiling range as thefeed, with the molecules having been rearranged o-r reformed into higheroctane-producing compounds. However, the extent of reforming of naphthaand naphtha-containing oils is usually limited owing to the formation ofexcessive coke as reaction temperature increases. For this reason, suchprocesses as catalytic and thermal reforming and the like are usuallydesigned to avoid excessive coke and dry gas make with, however, acorresponding limitation on the degree of naphtha improvementattainable. Upgrading of cleanliness of gum-forming properties is alsoquite important with certain olefinic naphthas, especially naphthasproduced in thermal cracking or coking operations. In this case,upgrading is usually accomplished by either passing the naphtha over' acatalytic cracking catalyst or by hydrofining. Again the first of thesealternates, i.e., catalytic cracking, results in an undesirable high gasand coke make; whereas the second, i.e., hydrofining, results in anoctane number loss.

Attempts at solving the above problems have generally involved one ormore hydro techniques, such as hydro- 3,337,447 Patented Aug. 22, 1967cracking, hydroforming, hydrodealkylation, etc., which processes tend toform lesser amounts of coke and dry gas while at the same time resultingin improved octane prod uct. However, indiscriminate use ofhydrocracking, for example, to upgrade naphthas, is oftenself-defeating, since products boiling below the range of the feed areformed, thereby lowering the naphtha yield. Hydroforming or catalyticreforming are also not practical with certain naphtha feeds, e.g., cokernaphthas, which contain appreciable sulfur, nitrogen and diolefins,again because of excessive coke make and rapid catalyst deactivation.Also, catalytic hydroforming, which depends upon aromatics formation foroctane improvements, is ineffective with feeds having low cycloparafiinconcentration.

It Will again be realized, therefore, that a conversion process which iscapable of selectively converting the low octane-producing components ofthe naphtha feed to lower boiling components which are readily removed,with -a minimum conversion of the high octane-producing components, isto be highly desired. Removal of the low octane components would thusresult in enhancement of the naphtha octane number without appreciablyaltering its boiling range.

It has accordingly been discovered that highly effective selectiveremoval of straight-chain hydrocarbons can be accomplished by the use ofcertain types of crystalline alumino-silicate zeolites having uniformpore openings of less than 6 Angstroms, preferably about 5 Angstroms.The essence of this invention resides in the surprising discovery that aparticular sulfided cation form of these S-Angstrom zeolites issubstantially superior to other forms. Specifically, it has been foundthat the S-Angstrom zeolite should be cadmium containing, preferablyhaving a major portion of its cation content supplied by a cadmiumcation, and most preferably having been ex changed solely with cadmiumcation for replacement of alkali metal originally in the zeolite.

It has been specifically found that naphthas may be successfullyupgraded by contacting them at suitable conditions of temperature andpressure in the presence of hydrogen with a sulfided cadmium-containingcrystalline metallo alumino-silicate zeolite having uniform effectivepore openings of less than 6 Angstroms, preferably about 5 Angstroms. Byupgrading is meant any hydro technique resulting in the formation of animproved or preferred product. This would include improved octane ratingand cleanliness, lower sulfur content, etc. The hydro techniquescontemplated include such processes as hydrofining, 'hydrocracking,hydrodealkylation, hydrogen transfer, etc., with the preferred processbeing hydrocracking. These processes will usually be con-ducted atelevated temperature and pressure in the presence of hydrogen.

It is fully recognized that the prior art has taught the use ofcrystalline alumino-silicate zeolites for cracking of various petroleumand hydrocarbon materials. For example, US. Patents Nos. 2,971,903 and2,971,904 disclose various hydrocarbon conversion processes employingcrystalline alumino-silicates having uniform pore openings between about6 and 15 Angstroms. As hereinbefore mentioned, the present inventionemploys crystalline aluminosilicates having uniform pore openings ofless than 6 Angstroms, preferably about 5 Angstroms, which pore size hasbeen found to be necessary and critical to the successful selectivehydrocracking herein contemplated. The prior art has also recognized thepossibility of se lectively converting normal parafiins by means ofS-Angstrom molecular sieves for such purposes as dewaxing, etc. Theseuses derive from the ability of these crystalline zeolite materials toselectively admit certain sized molecules into their pores whilerejecting others. Since these materials are now well-known adsorbentsand catalysts, they provide highly efiicient and valuable tools forselectively converting specified constituents of a hydrocarbon feed. Forexample, US. Patent No. 3,039,953 discloses the selective conversion ofnormal paraffins with a S-Angstrom zeolite. Also, U.S. Patent No.3,140,322 relates generally to selective catalytic conversion utilizingcrystalline zeolites and mentions dehydration, catalytic cracking,hydrogenation, etc.

The essence of the present invention, which distinguishes it from theabove prior art teachings, lies in the surprising discovery that certainunique S-Angstrom crystalline alumino-silicates are superior catalystcomponents for selective conversion reactions in general and selectivehydrocracking in particular. The cadmium cation-containing S-Angstromzeolite, with or without a metallic hydrogenation component, has astrikingly greater activity than similar catalysts based on othercationic forms of the zeolite.

A further distinction over these and similar teachings resides in thefact that the S-Angstrom crystalline alumino-silicate employed herein inthe cadmium cationexchanged form can be free of any metallichydrogenation catalyzing component and yet will surprisingly anduniquely exhibit selective hydrocracking activity. Reference to theaforementioned US. Patent No. 3,140,322, for example, indicates that theselective hydrogenation process therein disclosed was accomplished witha crystalline alumino-silicate zeolite catalyst having the usualmetallic hydrogenation component, such as platinum or palladium combinedtherewith. Again, the catalyst used in the present invention need notinclude such metallic hydrogenation component and yet, surprisingly, isa highly effective hydroconversion catalyst.

The process of the invention should also be distinguished from theconventional adsorption-desorption processes which are well known in theart. The present process involves a selective hydrocr-acking ofstraight-chain hydrocarbons. In the naphtha octane improvementembodiment, certain low octane-producing molecules, such asstraight-chain hydrocarbons, are selectively hydrocracked to gaseousmaterials, such as butane and lighter fractions, which are easilyremoved. The invention does not contemplate, therefore, a mechanicalseparation of diverse molecules, as accomplished by the conventionaladsorption-desorption phenomenon, In the case of selectivehydrocracking, converted products are not retained within the pores ofthe zeolite and a desorption step is unnecessary, thereby making theprocess economically attractive.

The crystalline metallo alumino-silicate zeolites having uniform poreopenings of about Angstroms contemplated for use in this invention arewell known and available in synthetic or natural form. For example, asuitable starting material, referred to as Zeolite A in US. Patent No.2,882,243, has a molar formula (dehydrated form) of where M is a metalusually sodium and n is its valence. It may be prepared by heating amixture containing Na O, A1 0 SiO and H 0 (supplied by suit-able sourcematerials) at a temperature of about 100 C. for 15 mmutes to 90 hours orlonger. Suitable ratios of these reactants are fully described in theaforementioned patent.

One suitable process for preparing such materials syntheticallyinvolves, for example, the mixing of sodium silicate, preferably sodiummetasilicate, with sodium aluminate under carefully controlledconditions. The sodium silicate employed should have a ratio of soda tosilica between about 0.8 to 1 and about 2 to 1, and the sodium aluminatemay have a ratio of soda to alumina in the range of from about 1 to 1 toabout 3 to 1. The amounts of the sodium silicate and sodium aluminatesolutions employed should be such that the ratio of silica to alumina inthe final mixture ranges from about 0.8 to 1 to about 3 to 1 andpreferably from about 1.1

to about 2.1. Preferably, the aluminate is added to the silicate atambient temperature with sufficient agitation to produce a homogeneousmixture. The mixture is then heated to a temperature of from about toabout 215 F. and held at that temperature for a period of from about 0.5to about 3 hours or longer. The crystals may be formed at lowertemperatures but longer reaction periods will be required. Attemperatures above about 250 F. a crystalline composition having therequisite uniform size pore openings is not obtained. During thecrystallization step, the pH of the solution should be main tained onthe alkaline side, at about 12 or higher. At lower pH levels, crystalshaving the desired properties are not as readily formed.

The products produced by the above procedure will have uniform poreopenings of about 4 Angstroms as produced in the sodium form. They maythen be converted to products having uniform pore openings of about 5Angstroms by replacement of the sodium via conventional ionexchangetechniques with various cations, such as calcium, magnesium cobalt,nickel, iron, manganese, etc., all of which are not suitable forpurposes of this invention.

Natural zeolites having effective pore diameters less than 6 Angstroms,and preferably about 5 Angstroms, are also herein contemplated and willinclude such materials as erionite, chabazite, analcite, lebrynite,natrolite, etc. Thus, both the natural and synthetic varieties of5-Angstrom zeolites are contemplated with the only limitation being oneof pore size. As indicated, the pore size must be sufficient tosubstantially admit the straightchain hydrocarbons but insufficient toadmit the valuable high octane-producing components, such as thearomatics, so as to avoid their hydrocracking. This capacity should,therefore, be demonstrated at the particular hydrocracking conditionscontemplated, since the effective pore diameter of these zeolitematerials often varies with temperature and pressure.

In accordance with the invention, it has been found that indiscriminateuse of the above-mentioned cations is not suitable for the selectivehydroconversion processes of the invention. More particularly, it hasbeen found that the use of cadmium cation is critical. Thus, thecatalyst used in the present invention is prepared from a crystallinealumino-silicate which, after cadmium cation exchange, has uniformeffective pore openings less than 6 Angstroms, and preferably about 5Angstroms, in diameter. The most preferred cation solution will be anaqueous solution of a cadmium salt, such as cadmium chloride or cadmiumnitrate. The extent of ion exchange should be sufficient to reduce thealkali metal, e.g., sodium content of the zeolite to less than 10 wt.percent, and preferably less than 5 wt. percent. The ion exchange isprefer ably conducted to cause at least 25%, and more prefer ablygreater than 50%, of the exchangeable cation content to be divalent byreplacement with the cadmium cation. It will be understood that althoughthe most preferred catalysts will be prepared by using cadmium cation asthe sole exchanging cation, the presence of cadmium together with otherexchanging cations will also be highly useful. Thus, in some of itsbroadest aspects, the present invention contemplates the use of about aS-Angstrom zeolite containing cadmium cation, Preferably, the zeolitewill have a major portion of its cation content supplied by cadmium withperhaps minor portions of residual sodium, as well as minor portions ofother ions which may also have been introduced via exchange for variouspurposes.

As a further option step in the preparation of the catalysts of theinvention, the catalyst can be combined with an active metallichydrogenation component which may be chosen from Groups V-B, VI-B,VII-B, or VIII of the Periodic Table and which is suitably exemplifiedby the metals cobalt, nickel, platinum, palladium, etc. Thehydrogenation component may be in the form of the free metal as in thecase of platinum group metals or as the oxide or sulfide as in the caseof cobalt, etc., or mixtures of such metals, oxides, or sulfides.Platinum group metals (i.e., metals of the platinum and palladiumseries) will be preferred for purposes of the present invention withpalladium being particularly preferred. Incorporation of thehydrogenation component may be accomplished by any conventionaltechnique, such as ion exchange followed by reduction, impregnation,etc. When palladium is employed, the cadmium-exchanged alumino-silicateis preferably impregnated with an ammoniacal solution of palladiumchloride sufficient to produce the desired amount of hydrogenation metalin the final product, and then dried and calcined at a temperature of800 to 1000 F. Reduction of the metal is then accomplished eitherseparately or in the hydrocracking reaction per se. The amount ofhydrogenation component may range from about 0.1 to about 25 wt.percent, based on the weight of final product. In the case of platinumgroup metals, e.g., palladium, the preferred amount will be in the rangeof about 0.1 to 6, e.g., 0.5 to 3 wt. percent, based on dry catalyst.

As an additional essential feature of the present invention, it has beenfound that the activity and effectiveness of the catalysts used hereinare critically dependent upon contact with sulfur prior to theirexposure to high temperature conditions employed in the selectiveconversion processes described herein. The catalyst is sulfactivated bycontact either with a sulfur-containing feed or, if the feed has a lowsulfur content, with hydrogen sulfide or an added sulfur compound whichis readily convertible to hydrogen sulfide at the hydroconditionsemployed, e.g., carbon disulfide, etc.

The extent of this sulfactivation treatment should be sufficient toincorporate 0.5 to 15 wt. percent sulfur into the catalyst. It has beenfurther found that the temperature to which the catalyst is subjectedduring the sulfactivation step is also critical and must be maintainedbelow about 1000 F., preferably 850 F., most preferably between about450 and 750 F. The effect of sulfactivation will be demonstrated in theexamples to follow.

The catalyst used in the present invention has been found to be highlyeffective for the upgrading of naphtha feeds, although the invention isnot to be so limited. Markedly improved octane number is achieved with avery low loss of naphtha yield. Additionally, the coke make produced inthe process is substantially lower than that experienced in catalyticcracking.

The feedstocks contemplated for use in the present invention may be anyof the typical petroleum hydrocarbon feeds, containing straight-chainhydrocarbons which are desirably removed for the particular intended useof the end product. For naphtha octane improvement, the feedscontemplated include either low-boiling naphtha or high boilingnaphtha-containing feeds, the latter typically having a boiling range ofabout 250 to 450, preferably 300 to 430 F. These feeds may beexemplified by virgin naphtha fractions, heavy coker naphtha, heavysteamcracked naphtha, heavy catalytic naphtha, and the like.

Typical hydrocracking conditions which are suitable for purposes of thepresent invention include a temperature of 400 to 950 F., preferably 650to 850 F.; a pressure of 200 to 4000, preferably 500 to 2500 p.s.i.g.; aspace velocity of 0.2 to 20, preferably 0.4 to 2 v./v./hr.; and ahydrogen rate of 1,000 to 10,000, preferably 1500 to 5000 standard cubicfeet of hydrogen per barrel of feed.

The invention will be further understood by reference to the followingexamples which are given for illustrative purposes.

EXAMPLE 1 This example illustrates the preparation and use of acadmium-containing crystalline alumino-silicate having uniform poreopenings of about 5 Angstroms in the selective hydrocracking of a C 'toC naphtha feed derived from an Arabian crude. The cadmium crystallinealumino-silicate was prepared as follows:

A charge of 500 grams of commercial sodium Zeolite A having poreopenings of about 4 Angstroms in diameter and a silica-to-alumina moleratio of about 2 to 1 was air-exposed overnight and then stirred in 2500ml. of distilled water containing one pound of cadmium chloride hydrate.After 18 hours the solution was replaced with a fresh portion andstirring was resumed for 24 hours. Again, the solution was replaced witha fresh portion and stirring was resumed for 24 hours. The slurry wasthen filtered, washed free of chloride ion, and dried at 150 C.overnight. The catalyst had a uniform pore size of about 5 Angstroms,and analyzed 1.67 wt. percent sodium and 30.60 wt. percent cadmium.

The above catalyst was presulfided prior to use in the selectivehydrocracking of the C to C naphtha feed. Specifically, the catalyst wascharged to a testing unit and sulfided with a mixture of'10% hydrogensulfide in hydrogen at the rate of 1.5 c.f./hr. for each cc. ofcatalyst. The temperature was maintained at 200 F. for two hours, thenraised at a rate of F./ hr. to 600 P. where it was held for one hour.The procedure is known to incorporate between 2.5 and 4.5 wt. percentsulfur into the catalyst.

The presulfided catalyst was then used to selectively hydrocrack a C toC naphtha feed having the following analysis at 850 F., 500 p.s.i.g.,0.5 v./v./hr. and 2000 s.c.f. H /B. The feed contained 0.25 wt. percentadded CS to ensure retention of the cadmium metal by the catalyst. Theresults of this run are summarized below:

The necessity of sulfiding the cadmium zeolite was demonstrated in anexperiment in which a 100 cc. portion of the fresh unsulfided catalystof Example 1 was used under the conditions of Example 1 but with noadded sulfur in the feed. Results obtained at 850 F., 500 p.s.i.g., 0.6v./v./hr., 1500 c.f./B exit hydrogen rate are compared with results ofExample 1 in the following tabulation:

TABLE II Product Feed None Sulfided Catalyst Preconditioning ProductDistribution, wt. Percent The two-fold increase (94.1 vs. 45) inconversion demonstrates quite dramatically the effect of presulfidingthe catalyst. Furthermore, it can be assumed that the effect of sulfuris more pronounced than demonstrated because the feed contained 83 ppm.sulfur which undoubtedly promoted the reaction and activated thecatalyst as the run progressed.

EXAMPLE 3 The effect of sulfur activation of cadmium zeolite A Wasfurther demonstrated. In this instance sodium zeolite A was ionexchanged at room temperature with cadmium chloride solution usingconcentrations disclosed in Example 1. A three-fold exchange for 21, 66and 20 hours, respectively, was made with each exchange followed bythree water washes. The product from the third wash after the thirdexchange was dried. A portion of the product was compacted into A -inchpellets and 170 cc. of the pellets were charged to a fixed bed testingunit. The catalyst was heated to 300 F. in a stream of nitrogen and thenhydrogen at atmospheric pressure. The system was then maintained forabout 64 hours at 400 F. with hydrogen flow at atmospheric pressure. Thereupon, the system was pressurized with hydrogen at 500 p.s.i.g. andupon increasing the temperature to 500 F. the C to C feed of Example 1,containing 1% carbon disulfide, was introduced. Conversion was conductedat 500 p.s.i.g., 0.5 v./v./hr., and an exit hydrogen rate of 1895c.f./B. The temperature was varied over different time periods, asfollows:

Period Run, hours Temperature, F.

A (P0. 5 500-550 B 0. 5'2. 5 550-725 2. 531. 5 725*850 3. 5-5. 5 850 Cc- 5. 56. 5 850 Products from Periods B and C were segregated foranalyses and a subsequent Period D was made under the same conditions asPeriod C, except that the feed contained 0.25 wt. percent added carbondisulfide. A decided improvement in removal of normal parafiins withcontinued exposure to the sulfur-containing feed was observed andclearly demonstrates increasing activation of the catalyst, as indicatedbelow:

As demonstrated in Example 2, presulfiding of the cadmium-containingS-Angstrom zeolite catalysts is necessary and critical to theirsuccessful use. When presulfided in accordance with the invention,markedly superior cata lysts are formed, which are substantially moreselective and active than another recently discovered similar selectiveand active than another recently discovered similar selectivehydro-conversion catalyst. In copending applications Ser. Nos. 444,812and 444,796 both filed April 1, 1965, the surprising and unexpectedsuperiority of zinccontaining S-Angstrom crystalline zeolites isdisclosed. In these applications comparison of the zinc form to suchother forms as calcium, magnesium, nickel, etc., is made with the clearconclusion that Zinc is the preferred zeolite form. It is further showntherein that when the zeolite is further combined with a hydrogenationmetal, such as palladium, the activity and selectivity of the catalystincrease further.

In order to compare the relative selective catalytic abilities of therecently discovered superior palladiumzinc S-Angstrom zeolite of theaforementioned application Ser. No. 444,796 with the cadmium S-Angstromzeolite of the present invention, a palladium-zinc S-Angstrom zeoliteprepared in substantial accordance with the procedure described on pages13 and 14 of copending application Ser. No. 444,796 was utilized, afterpresulfiding in hydrocracking operation with a light naphtha feedcontaining 0.25 wt. percent carbon disulfide, at 700 to 850 F., and 500to 1000 p.s.i.g., to selectively hydrocrack the C to C naphtha feed ofExample 1. Under comparable conditions of temperature, pressure, feedrate and hydrogen rate, the following comparison with the results ofExample 1 was obtained.

TABLE IV Product Feed Cadmium Palladium-omZinc 5-Angstrom Zeolite5-Angstrom Zeolite Conversion of 1105 and 1100 As indicated, thepresulfided cadmium-containing 5- Angstrom sieve showed greaterselectivity at approximately the same conversion level, as particularlyindicated by the higher n-pentane conversion. It is further noteworthythat the cadmium S-Angrstom zeolite exhibited this superiority even inthe absence of the palladium hydrogenation component, which wouldordinarily be expected to be necessary in hydrocracking reactions.

It will be understood that the above description is to be consideredillustrative and that variations can be made by those skilled in the artwithout departing from the spirit of the invention.

What is claimed is:

1. A process for reducing the straight-chain hydrocarbon content of ahydrocarbon feedstock by selectively hydrocracking same which comprisescontacting said feedstock at elevated temperature and pressure in thepresence of hydrogen with a catalyst comprising a crystallinealumino-silicate zeolite containing cadmium in an amount correspondingto at least 25% of its cationic content and having uniform pore openingsof about 5 Angstrom units, wherein said catalyst contains 0.5 to 15 wt.percent sulfur, and recovering a hydrocarbon product having asubstantially reduced straight-chain hydrocarbon content.

2. The process of claim 1 wherein said feedstock is a naphtha fraction.

3. The process of claim 1 wherein the sodium content of said zeolite isless than about 10 wt. percent.

4. The process of claim 1 wherein a major proportion of the cationcontent of said zeolite is supplied by cadmium cation.

5. The process of claim 1 wherein said catalyst has been sulfactivatedby treatment with a sulfur compound.

6. The process of claim 1 wherein said catalyst additionally comprises ahydrogenation component.

7. The process of claim 6 wherein said hydrogenation component is aplatinum group metal.

8. The process of claim 7 wherein said platinum group metal ispalladium.

9. The process of claim 6 wherein said catalyst is sulfactivated bycontact with a sulfur-containing feedstock.

10. A catalyst composition comprising a metallic hydrogenation componentcombined with a crystalline alumino-silicate zeolite containing cadmiumin an amount corresponding to at least 25% of its cationic content andhaving uniform pore openings of about Angstrom units, said catalystcomposition additionally comprising 0.5 to 15 wt. percent sulfur.

11. The composition of claim 10 wherein said hydrogenation componentcomprises a platinum group metal.

12. The composition of claim 11 wherein said platinum group metal ispalladium.

13. A process for improving the octane rating of naphtha fractions byselective hydrocracking of straightchain hydrocarbons contained thereinwhich comprises contacting said naphtha fractions at elevatedtemperature and pressure in the presence of hydrogen with a catalystcomprising a crystalline alumino-silicate zeolite having uniform poreopenings of about 5 Angrstoms, said zeolite having at least 25% of itscation content supplied by cadmium cation, said catalyst containing 0.5to 15 wt. percent sulfur, and recovering a naphtha product havingsubstantially reduced straight-chain hydrocarbon content and an improvedoctane rating.

14. The process of claim 13, wherein said zeolite has a major proportionof its cation content supplied by cadmium cation.

15. The process of claim .13, wherein said catalyst additionallycomprises a hydrogenation component.

16. The process of claim 15, wherein said hydrogenation component is aplatinum group metal.

17. The process of claim 13, wherein said catalyst has beensulfactivated by contact with a sulfur-containing feedstock.

18. The process of claim 13, wherein said temperature is within therange of 400 to 950 F., said pressure is within the range of 200 to 4000p.s.i.g., and wherein the hydrogen feed rate is 1000 to 10,000 s.c.f./B.of naphtha feed.

19. The process of claim 13, wherein said temperature is within therange of 650 to 850 F., said pressure is within the range of 500 to 2500p.s.i.g., and wherein the hydrogen feed rate is 1500 to 5000 s.c.f./B.of feed.

20. A process for selectively hydrocracking naphtha fractions containingstraight-chain hydrocarbons and nonstraight-chain hydrocarbons, whichcomprises contacting said fractions in a catalyst zone maintained atelevated temperature and pressure, flowing a substantial amount ofhydrogen gas into said pressurized catalyst zone, and recovering naphthaproduct having a substantially reduced straight-chain hydrocarboncontent and a substantially improved motor octane rating, wherein. thecatalyst in said zone comprises a sulfactivated crystallinealumino-silicate zeolite having uniform pore openings of about 5Angstrom units and containing cadmium in an amount corresponding to atleast 25% of its cationic content and further containing 0.5 to 15 wt.percent sulfur.

21. The process of claim 20, wherein said catalyst additionallycomprises a metallic hydrogenation component.

22. The process of claim 20, wherein said temperature is within therange of 650 to 850 F., and said pressure is Within the range of 500 to2500 p.s.i.g.

References Cited UNITED STATES PATENTS 2,971,904 2/1961 Gladrow et al.208-135 3,013,983 12/1961 Breck et al. 252455 3,039,953 6/1962 Eng 208263,175,967 3/1965 Miale et al. 208 3,243,366 3/1966 Kimberlin et al.20828 DELBERT E. GANTZ, Primary Examiner. HERBERT LEVIN, Examiner.

1. A PROCESS FOR REDUCING THE STRAIGHT-CHAIN HYDROCARBON CONTENT OF AHYDROCARBON FEEDSTOCK BY SELECTIVELY HYDROCRACKING SAME WHICH COMPRISESCONTACTING SAID FEEDSTOCK AT ELEVATED TEMPERATURE AND PRESSURE IN THEPRESENCE OF HYDROGEN WITH A CATALYST COMPRISING A CRYSTALLINEALUMINO-SILICATE ZEOLITE CONTAINING CADMIUM IN AN AMOUNT CORRESPONDINGTO AT LEAST 25% OF ITS CATIONIC CONTENT AND HAVING UNIFORM PORE OPENINGSOF ABOUT 5 ANGSTROM UNITS, WHEREIN SAID CATALYST CONTAINS 0.5 TO 15 WT.PERCENT SUFLUR, AND RECOVERING A HYDROCARBON PRODUCT HAVING ASUBSTANTIALLY REDUCED STRAIGHT-CHAIN HYDROCARBON CONTENT.